The present invention is a vegetable wax comprising triglycerides. Particularly, the present invention is used as an additive in boxboard coatings and adhesives, either by itself or as part of a composition, to render the coating or adhesive dispersible in warm alkaline water.
Petroleum waxes, such as paraffin and microcrystalline wax, and synthetic waxes such as Fischer Tropsch (xe2x80x9cFTxe2x80x9d) and polyethylene, are used extensively in paper coatings to impart moisture resistance and enhanced moisture vapor barrier properties to the paper. Waxes used for this purpose tend to be low viscosity ( less than 1,000 cps @ 284 degrees F) and have relatively low melting temperatures ( less than 302 degrees F).
Large oil companies such as Shell Oil, ExxonMobil and other oil refiners supply petroleum waxes used in these applications. Most of this wax is derived in the process of refining lube oil where the wax is separated from the lube oil stock and refined into various fractions of wax including paraffins, and microcrystalline waxes. Formulators such as Astor Wax, IGI and Moore and Munger also supply wax for these applications that is either resold as is from the oil companies, and/or formulated and repackaged to meet the specific needs of customers. The two largest suppliers of FT waxes are Sasol from South Africa and Shell Oil from Malaysia. The waxes are sometimes formulated with other ingredients to modify their properties for specific applications. Such modifiers include resins to improve strength and toughness or improve flexibility or gloss.
These waxes are also used extensively in adhesives, whose formulations usually incorporate a resin (such as ethylene vinyl acetate xe2x80x9cEVAxe2x80x9d, or polyethylene) and a tackifier (such as a rosin ester, or tall oil fatty acid derivatives) to provide a coating that can bond or seal paper articles. Waxes are used in adhesive coatings to provide additional functionality to the adhesive coating, such as set speed and thermal stability.
A common characteristic of waxes used in coating paper and formulating adhesives is that they have a relatively low viscosity to enable flow of the coating or adhesive and its penetration of the cellulosic fiber. Typical viscosity ranges of waxes used in these applications are from about 10 SUS (Seybolt method) at 210 F to about 300 SUS at 300 F. In general, the lower the viscosity, the better the penetration into the cellulosic substrate. Better penetration is generally desirable for good adhesion.
Waxes used in coating paper and formulating adhesives can be used alone, but more commonly are formulated with other materials to modify and enhance their properties. Such materials used as additives might include antioxidants (such as butylated hydroxy toluene xe2x80x9cBHTxe2x80x9d, and other free radical scavenger materials), coupling agents (maleic modified polymers), gloss enhancing agents, and additives for rendering the coating more flexible (ethylene or ethylene vinyl acetate copolymers) are among some of the more commonly used modifiers for wax coatings.
Many different types of cellulosic materials are coated with petroleum and synthetic waxes to impart moisture resistance and adhesive properties. Wax coating techniques are well understood to those skilled in the art. Wax coating can involve immersion of the cellulosic material in a molten bath of the wax. It can also involve cascade and curtain coating where a thin layer of molten wax is allowed to flow onto the cellulosic material. See, for example, Sandvick et al. (U.S. Pat. No. 5,491,190, incorporated by reference herein). Other techniques are also used depending on the desired placement of the wax on the cellulosic material.
Coating and adhesive formulations containing petroleum and/or synthetic waxes present an inherent problem when paper products containing these compounds are recycled to recover the fiber components for reuse. Recycling paper involves mixing the paper to be recycled with warm water, usually with a pH in the alkaline range ( greater than pH7). When wax is present in the recycled paper, the wax does not solubilize but forms what is known in the trade as xe2x80x98stickiesxe2x80x99. The xe2x80x9cstickiesxe2x80x9d is material that causes paper processing and forming machinery to become dirty and have gum like deposits, which cause maintenance and other problems for paper manufacturers. In addition, the xe2x80x98stickiesxe2x80x99 deposit on the recycled paper, tending to form unsightly spots and thus causing the recycled paper to have a lower commercial value, and in some cases, not to be useable at all (See, for example, Watanabe et al., U.S. Pat. No. 6,117,563).
Various techniques have been used in attempts to overcome the problem of removing petroleum and synthetic waxes in the process of recycling paper. Various additives to the wax have been tried (U.S. Pat. Nos. 6,273,993, 6,255,375, 6,113,738, 5,700,516, 5,635,279, 5,539,035, 5,541,246, 6,007,910, 5,587,202, 5,744,538, 5,626,945, 5,491,190, 5,599,596). These patents are incorporated here by reference.
For example, Michelman (U.S. Pat. No. 6,255,375 B1) discloses incorporation of at least one chemical compound which is either itself capable of acting as a latent dispersant for the coating, or capable of being chemically modified so as to act as a dispersant, thus rendering the hot melt coating more readily dispersible from the coated product.
Chiu (U.S. Pat. No. 6,113,729) discloses using hydrogen peroxide with various waxes to produce laminated wood products with a light color.
Ma et al. (U.S. Pat. No. 5,635,279) discloses inclusion of a polystyrene-butadiene polymer, in combination with a paraffin or polyethylene wax emulsion, for treating paper products.
Miller et al. (U.S. Pat. No. 5,744,538) disclose a low molecular weight, branched copolyester for use in an adhesive.
Sandvick et al. (U.S. Pat. Nos. 5,491,190, 5,599,696 and 5,700,516) disclose compositions comprising ethylenically unsaturated monocarboxylic acids in combination with either a fatty acid or paraffin wax to render paper products water resistant and repulpable.
Severtsen et al. (U.S. Pat. No. 6,113,738) disclose the addition of plasticizers, dispersants or wetting agents to the recycling mixture to facilitate wax breakdown and dispersion.
Vemula (U.S. Pat. No. 5,891,303) discloses a process using a heated solvent, n-hexane, to remove wax from waste paper, and indicates that both the wax and the paper can be recovered from the recycling process.
In addition there have been mechanical techniques used in an attempt to recycle wax containing paper products through processes such as floating the wax from the slurried paper mix. Heise et al. (U.S. Pat. No. 6,228,212 B1) disclose a method to remove wax from paper during recycling, using a combination of floatation and filtration. They note that the majority of waxes used in the paper industry are petroleum-based waxes. Because none of these techniques are commercially viable, it is still customary in many locations to isolate wax coated paper products and send them to a landfill or to an incinerator in lieu of recycling them (Heise et al., U.S. Pat. No. 6,228,212 B1).
The prior art thus illustrates the use of petroleum derived waxes, synthetic waxes, and certain vegetable waxes for rendering cellulosic articles water resistant, or for their inclusion in adhesives for attachment of cellulosic articles. However, the problem of recycling articles containing these compositions remains. Therefore, there is a need for employing a composition, which has the barrier and physical properties of petroleum derived or synthetic waxes while allowing for the economical recycling of fibrous cellulosic materials, which have incorporated these waxes as coatings and/or adhesives. Due the large volume of waxes consumed in these applications it is also preferred that the compositions be readily available. From both a supply and a natural resource viewpoint, it is preferred that the compositions be obtained from a source that preferably is renewable, such as from plant extracts.
It is also known through experience with synthetic low molecular weight ethylene based polymers that have wax-like characteristics, that as more functionality is added to the wax-like polymer, by the addition of ester and/or carboxyl groups, the polymer wax can be made increasingly soluble in alkaline water. Functionality of low molecular weight synthetic polymers can be increased by co-polymerization and/or grafting co-monomers such as acrylic acid into the polymer. The saponification value of a polymer, as measured by the amount of KOH needed to neutralize one gram of polymer, is a good measurement of both carboxyl and ester functionality of a polymer. It is known that as the saponification value begins to exceed about 130 mgKOH/gm, the polymer will start to solubilize in warm alkaline water. Pure acrylic polymers are very functional and have good solubility in water. These synthetic polymers with wax-like characteristics and functional groups are not widely used in wax coating and adhesive formulations due to their excessive cost to manufacture and their inherent undesirable properties such as relatively high viscosity and their being relatively soft.
The present invention is a natural wax for use in paper coatings and paper adhesives. The product is a commercially available high triglyceride wax derived from the processing of natural oil containing commodities such as soybeans, palm and other crops from which oil can be obtained. The materials are processed and supplied by Archer Daniels Midland (Decatur Ill.) designated by their product number 86-197-0, Cargill Incorporated (Wayzata, Minn.) designated by their product number 800mrcs0000u and other sources under a generic name xe2x80x98hydrogenated soybean oilxe2x80x99. Palm oil wax was supplied by Custom Shortenings and Oils (Richmond, Va.) and was desigiated as their product Master Chef Stable Flake-P.
It is an object of the present invention to provide a composition that can be applied to fibrous cellulosic objects such as paper and paperboard, and render such treated cellulosic objects recyclable using conventional means of recycling.
It is an object of the present invention to provide a material that can be coated on fibrous cellulosic objects such as paper and paperboard, using conventional coating means.
Another object of the present invention is to provide a composition which when applied to fibrous cellulosic objects imparts barrier properties required to protect the cellulosic object and/or it contents from moisture.
Still another object of the present invention is to provide a composition which when applied to fibrous cellulosic objects and renders those cellulosic objects water resistant, can then be removed from the treated cellulosic objects using conventional methods of recycling fibrous cellulosic materials without having the deleterious effects associated with conventional petroleum and or synthetic waxes.
Yet another object of the present invention is to provide a composition which can be derived from a renewable resource in place of non-renewable petroleum based compositions.
Another object of the present invention is to provide a composition which can replace the petroleum and/or synthetic wax component of an adhesive formulation with a composition that can render the adhesive repulpable without impairing the adhesive properties of the formulation.
Still another object of the present invention is to provide a renewable source of moisture resistant wax, which can be economically produced.
Another object of the present invention is to provide a composition for use in paper coating and/or adhesive that is generally regarded as safe by the Food and Drug Administration.
The present inventors have unexpectedly discovered that highly hydrogenated oils such as palm and soybean can be converted into a wax that can be used effectively as substitutes for conventional petroleum and synthetic waxes in the coating of cellulosic materials with the ability to recycle those cellulosic materials through commercially available means.
The present invention relates to a coating composition of a highly hydrogenated vegetable oil (palm, soybean, corn) that has wax-like properties and can be coated on cellulosic materials such as paper and paperboard through conventional means and subsequently removed through commercially practiced recycling techniques. The hydrogenated oils that can be used are  greater than 90% triglyceride and have a range of carbon numbers with C18 being the most predominant component ( greater than 50%).
The present invention comprises waxes prepared from hydrogenated plant oils, such as palm and soybean, that are used to render cellulosic materials resistant to water. Unlike cellulosic materials rendered water resistant with waxes obtained using petroleum-derived or synthetic waxes, the water resistant cellulosic materials prepared using this composition are recyclable using conventional paper recycling methods; the composition is dispersible in warm water solutions. Such water resistant materials are characterized by enhanced moisture barrier properties. The compositions have a low iodine value (between 2-5), and melting points between approximately 120-165 degrees F (Mettler Drop Point). The wax comprises a triglyceride whose fatty acids are predominantly stearic acid (C18). The composition is used as an additive in the manufacture of wax coated boxes and adhesive compounds used in boxboard packaging and manufacturing operations.